In this competitive renewal, we propose to extend our twin study of individual differences in executive functions (EFs) by conducting the following: (1) the first assessment of genetic and environmental contributions to stability and change in EFs during the transition from adolescence to young adulthood;(2) the first study of the relations among self-regulation abilities in three domains, as well as the genetic and environmental etiologies of individual differences in these self-regulation abilities in early adulthood;and (3) the first behavioral genetic study of the relationship between EFs and self-regulation in early adulthood. By retesting participants on the tasks used to construct latent variable measures of the three EFs currently assessed (Inhibiting, Updating, and Shifting), we will be able to test the hypothesis that stable trait variance in EFs is genetically determined, while changes (e.g., declines) are environmentally influenced, for example by drug use. We will also use data from a theoretically motivated battery of self-regulation measures to conduct the first study of the relations among self-regulation abilities in three domains cognitive, emotional, and behavioral as well as the genetic and environmental etiologies of individual differences in these self- regulation abilities in early adulthood. Finally, we will use the measures of the three EFs, as well as data on two additional EFs (Resisting Proactive Interference and Dual-Tasking) to examine the relations of these EFs to the three domains of self regulation. To achieve these aims, we will re-assess the three EFs in a target sample of 814 individual twins from 214 monozygotic and 193 dizygotic pairs who have participated in the Colorado Longitudinal Twin Study (LTS) since infancy. In the first grant period, we have now tested 698 individual twins ages 16.5-19 years, 48 more than our original goal of 650, and during the no-cost-extension we will attempt to test an additional 116 twins. With our attrition assumptions, we anticipate a final sample of 365 pairs tested at both Wave 1 and Wave 2 (age 21 to 23 years). We will use phenotypic factor analyses and multivariate genetic and environmental structural equation modeling to address the three specific aims. PUBLIC HEALTH RELEVANCE: This is a twin study of the etiologies of stability and change in cognitive executive functions during adolescence and early adulthood, together with individual differences in the ability to regulate one's own behavior. These differences may contribute to mental health generally and to health (e.g. obesity), psychological (e.g. depression), and behavioral (e.g. substance abuse) problems.